I suspect you are just being tripped up by time zones and the International Date Line.

Because Japan was on the "New Day" side of the line it was December 8th there when Nagumo launched the attack. For example it is currently 1030 on the East Coast, 0430 in Hawaii and 2330 in Tokyo, about to be Tuesday Morning.

So if they waited to put together a special edition with the full text of the declaration, and to have initial reports from the attacks it likely would have taken all day. The Japanese Press was rigidly under the thumb of the military, to the extent of public reprimands to writers and editors over even minor changes in wording from what the Army or Navy handed them, while official government proclamations, and Imperial Rescripts were given the most stringent quality control, so as not to misquote his majesty.

As for FDR's knowledge of the attacks and how it grew it was already early afternoon when word arrived, mostly by phone. Roosevelt was in the Yellow Room, his preferred place of work and study on the 2nd Floor of the WH(he would often take breaks and enjoy his stamp collection, or his deep love of all things naval and nautical furnishing the room).

Quickly arriving were SECNAV Knox, CNO Admiral Stark, and Admiral King Commander of the Atlantic Fleet. Updates would come in by secure phone line from Pacific Fleet HQ and Admiral Kimmel's office at Pearl, and as the true magnitude of the attack appeared the mood grew worse and worse.

FDR was a Navy man at heart, perhaps even more so than he was President, he knew his ships, and even knew who was captaining them, and was visibly struck and hurt when he found out finally just how bad it all was.

That night the Office of the President issued a short Press Notice, confirming the attack, and stalling more until the Joint Session of Congress the next day. Secretary Knox also gave a few short words to the Press to that extent too.

Ian W. Toll's Pacific Crucible gives a very solid overview of the evolving knowledge in DC that afternoon if you are interested.

Do you have the newspaper in your possession now? Would it be possible to scan the front page, or else take a photo and share that? It would perhaps be helpful in answering the question!

I would be interested in looking at the front page, but the simple answer is that many US newspapers in 1941 interpreted the attack as a declaration of war, as in fact the US government did.

There's also the possibility that the edition you're looking at is an extra or an evening edition -- in the days before the Internet, the only way to update subscribers on breaking news (besides radio, of course, or headlines updated on the newspaper's windows) was to print an extra edition of the paper. But it looks like the "extra" edition of the Oregon Journal for that day doesn't have the same headline you're asking about.

What I've read is that Pearl Harbor happened that morning. In the newspaper, there's an article that simple says "The White House said tonight that Navy reports from Hawaii indicated that heavy loss of life and damage resulted from an early morning Japanese air raid attack."

What does "said tonight" refer to? I thought it wasn't attacked until Sunday morning?

The attack on Pearl Harbor commenced around 7:55 a.m. Dec. 7, Hawaii time, or 12:55 p.m. in the Eastern time zone. The news of the attack also took some time to filter back into the general consciousness, and the White House was busy coordinating responses to not only that attack but other attacks in the Pacific. So, keep in mind that "tonight" modifies "White House said," not the attack, which it says happened in the morning.

Another way to think of it would be to say "Tonight, the news from the White House is ..."

(In case you're wondering why I'm posting outside my flair area, I have worked in journalism most of my life and actually studied newspapers in a history graduate program, but ships are more interesting.)

Okay, in posting this comment as a final results sort of comment. Our conclusion is this:

Thanks to /u/jschooltiger and /u/DBHT14, does this look good?

Sunday, Dec. 7.

Approx. 4:00 am US (Oregon), 1:00 am Hawaii, 8:00 pm Japan

Standard Sunday newspaper is released, doesn't include Japan war declaration or details of Pearl Harbor, as the attack would not occur for another few hours. it's expected that Japan will declare war, but no official word.

*Sunday, Dec. 7.*
>Approx. 10:00 am US (Oregon), 7:00 am Hawaii

*Monday, Dec. 8*
>Approx. 2:00 am Japan

Pearl Harbor is attacked. Word comes to the US and is being processed. Most assume this means war, but no official word from Japan.

Evening: President states that heavy loss of life occurred at Hawaii. Holds/calls meeting with cabinet. (line 2 and 3 of newspaper source picture)

**Possible first extra printed here?**
 

Sunday, Dec. 7.

Approx. 11:00 pm US (Oregon), 8:00 pm Hawaii 9:00 pm Japan

Monday, Dec. 8

Approx 6:00 am Japan

Japan releases statement officially declaring war on US, Britain. Misprinted in line 1 of newspaper source picture as 'Monday, Dec. 9', should read as Monday, Dec. 8. Also misprinted Tokyo as 'Toyyo'

My 'second extra' edition of newspaper printed soon after here with knowledge of official declaration of war, attack on Pearl Harbor.